A data storage device including a non-volatile semiconductor memory such as a solid state drive (SSD) carries out a refresh write process (memory refresh) to prevent data loss. The refresh write process is a process of writing at least all valid data stored in a target block of the non-volatile semiconductor memory into a different block thereof.
The refresh write process may be carried out with higher priority over other processes to shorten time to be completed the refresh write process. However, if a controller of the data storage device performs the refresh write process without any limitations or restrictions, then latency with respect to data writing requests from a host may increase.